Project description:To explore the mechanisms governing the leaf color variations in Chinese orchids, we analyzed gene expression differences between a wild-type and an albino-type cultivar of Cymbidium longibracteatum
Project description:The study of orchid mycorrhizal interactions is particularly complex because of the peculiar life cycle of these plants and their diverse trophic strategies. Here, large-scale transcriptomics has been applied to investigate gene expression in the mycorrhizal roots of the terrestrial mixotrophic orchid Limodorum abortivum under natural conditions. Our results provide new insights into the mechanisms underlying plant-fungus interactions in orchids and in particular on the plant responses to the mycorrhizal symbiont(s) in adult roots. Comparison with gene expression in mycorrhizal roots of another orchid species, Oeceoclades maculata, suggests that amino acids may represent the main nitrogen source in both protocorms and adult orchids, at least for mixotrophic species. The upregulation, in mycorrhizal L. abortivum roots, of some symbiotic molecular marker genes identified in mycorrhizal roots from other orchids as well as in arbuscular mycorrhiza, suggests a common plant core of genes in endomycorrhizal symbioses. Further efforts will be required to understand whether the specificities of orchid mycorrhiza depend on fine-tuned regulation of these common components, or whether specific additional genes are involved.
Project description:We report that phosphatidylglycerol (PG) biosynthesis in plastid is required for plastid gene expression mediated by plastid-encoded RNA polymerase and light-induced expression of nuclear-encoded photosynthesis-associated genes. A transcription factor GOLDEN-LIKE1 was also found to be involved in the downregulation of nuclear photosynthesis genes in responce to PG deficiency.
Project description:The unicellular, free-living, nonphotosynthetic chlorophycean alga Polytomella parva, closely related to Chlamydomonas reinhardtii and Volvox carteri, contains colorless, starch-storing plastids. The P. parva plastids lack all light-dependent processes but maintain crucial metabolic pathways. The colorless alga also lacks a plastid genome, meaning no transcription or translation should occur inside the organelle. Here, using an algal fraction enriched in plastids as well as publicly available transcriptome data, we provide a proteomic characterization of the P. parva plastid, ultimately identifying several plastid proteins, both by mass spectrometry and bioinformatic analyses. Altogether these results led us to propose a plastid proteome for P. parva, i.e., a set of proteins that participate in carbohydrate metabolism; in the synthesis and degradation of starch, amino acids and lipids; in the biosynthesis of terpenoids and tetrapyrroles; in solute transport and protein translocation; and in redox homeostasis. This is the first detailed plastid proteome from a unicellular, free-living colorless alga.
Project description:Plastids are endosymbiotic organelles containing their own genomes, which are transcribed by two types of RNA polymerases. One of those enzymes is a bacterial-type, multi-subunit polymerase encoded by the plastid genome. The plastid-encoded polymerase (PEP) is required for efficient expression of genes encoding proteins involved in photosynthesis. Despite the importance of PEP, its DNA binding locations have not been studied on the genome-wide scale at high resolution. We established a highly specific approach to detect the genome-wide pattern of PEP binding to chloroplasts DNA using ptChIP-seq. We found that in mature Arabidopsis thaliana chloroplasts, PEP has a complex pattern of binding to DNA with preferential association at genes encoding rRNA, tRNA and a subset of photosynthetic proteins. Sigma factors SIG2 and SIG6 strongly impact PEP binding to a subset of tRNA genes and have more moderate effects on PEP binding throughout the rest of the genome. PEP binding is commonly enriched on gene promoters, around transcription start sites. Finally, the levels of PEP binding to DNA are correlated with the levels of RNA accumulation, which allowed estimating the quantitative contribution of transcription to RNA accumulation.
Project description:We use Arabidopsis thaliana embryogenesis as a model system for studying intercellular transport via plasmodesmata (PD). A forward genetic screen for altered PD transport identified ise1 and ise2 mutants with increased intercellular transport of fluorescent 10-kDa tracers. Both ise1 and ise2 exhibit increased formation of twinned and branched PD. ISE1 encodes a mitochondrial DEAD-box RNA helicase, while ISE2 encodes a DEVH-type RNA helicase. Here we show that ISE2 foci are localized to the chloroplast stroma. Surprisingly, plastid development is defective in both ise1 and ise2 mutant embryos. In an effort to understand how RNA helicases that localize to different organelles have similar impacts on plastid and PD development/function we performed whole genome expression analyses. The most significantly affected class of transcripts in both mutants encodes products that target to and enable plastid function. These results reinforce the importance of plastid-mitochondria-nucleus crosstalk, add PD as a critical player in the plant cell communication network, and thereby illuminate a new signaling pathway, dubbed organelle-nucleus-plasmodesmata signaling (ONPS). Several genes with roles in cell wall synthesis and modification are also differentially expressed in both mutants, providing new targets for investigating PD development and function.